Stem cell factor ("SCF", see PCT Pub. No. WO 91/05795; also called kit-ligand, PCT Pub. No. WO 92/03459, mast cell growth factor, see PCT Pub. WO 92/00376 and Steel factor (or "SF" or "SLF") White, Cell 63: 5-6 (1990)) is hematopoietic factor which acts on hematopoietic progenitor cells. The gene encoding SCF has been cloned and expressed, e.g., Martin, et al., Cell 63: 203-211 (1990), and PCT Pub. No. WO 91/05795, which is herein incorporated by reference in its entirety.
One hallmark of SCF activity is expansion of primitive progenitor cells in the marrow and peripheral blood. Clinically, SCF may prove useful in a number of disease settings where myelosuppression results in significant morbidity and mortality. These settings include the use of SCF in: mobilizing progenitor cells for use in transplantation following myeloablative chemotherapy, priming the marrow before bone-marrow harvest for autologous bone marrow transplantation, and in accelerating hematopoietic reconstitution following standard-dose chemotherapy or myeloablative chemotherapy/total body irradiation.
SCF has numerous active forms, including a membrane bound version and a soluble version. See PCT Pub. No. 91/05795. C-terminal deletion analogs also have activity. For example, SCF 1-137 (with "1" referring to the first amino acid of the mature protein) demonstrates biological activity, and SCF 1-141 demonstrates more or less full biological activity. Langley et al., Arch. Biochem. Biophys. 311: 55-61 (1994). SCF 1-165 having an aspartic acid at position 10, instead of an asparagine as in the native sequence (referred to as "N10D") has also been studied, and found to not appreciably influence the rate of dimer formation. Lu et al., Biochem. J. 305: 563-568 (1995). Certain covalently linked SCF dimers are reported in PCT publication WO 95/26199. Stability is reportedly increased by an intermolecular covalent linkages.
SCF analogs with increased biological activity and stability, such as those provided herein, would be desirable for consumers, as lower dosages may be used to achieve the same biological result. Such analogs would be desirable for producers, as a more active product results in more units of product being sold per production batch. Increased stability, particularly increased shelf-life, would be particularly useful for both consumers and producers. Thus, the present invention provides these advantages and satisfies the needs of consumers and producers.